NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Cash and Cash Equivalents (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in the allowance for doubtful accounts
Beginning balance	$ 1.2	$ 0.2
Provision, charged to expense	3.7	1.1	$ 0.2
Write-off, less recoveries	(1.4)	(0.1)
Ending balance	$ 3.5	$ 1.2	$ 0.2